<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>输入圆的周长计算面积和周长</title>
</head>
<body>
    <div>圆的半径：<input id="r" type="text"></div>
    <div>圆的周长：<input id="c" type="text"></div>
    <div>圆的面积：<input id="s" type="text"></div>
    <script>
        var r=prompt("请输入圆的半径:");
        if(!isNaN(r)){
            var c=Math.PI*2*r;
            var s=Math.PI*r*r;
            document.getElementById("r").value=r;
            document.getElementById("c").value=c.toFixed(2);
            document.getElementById("s").value=s.toFixed(2);

        }else{
            alert("请输入正确的数字");
        }

    </script>
</body>
</html>